This invention relates to new and useful improvements in bolt constructions and to a process of forming the same.
Several processes of producing bolts have heretofore been used. One process comprises forming the bolts in screw machines. This involves utilizing a metal bar of outside dimensions equivalent to the outside dimensions of the finished bolt head. The metal bar is rotated in the screw machine and tools contacting the rotating bar cut away the material under the head to form a bolt shank of a desired diameter. After other tools cut threads on the shank, the bolt is then cut away from the rotating bar. The screw machine process has several disadvantages, namely, it is relatively slow and expensive, it produces a great amount of scrap metal, and the grain of the metal in the bolt as formed is weakened due to the lateral cutting thereof at the base of the head.
Another process of producing bolts comprises the hot heading process. It consists of forcing heated metal into dies to form the desired shape. The utilization of dies for withstanding the high temperatures necessary and the necessity of providing equipment for producing such temperatures in the process makes for greater costs and complications.
Still another process of producing bolts and the one mostly used is the cold heading process. This process involves a system of stationary and movable dies utilizing round stock of a diameter to suit the finished thread diameter of the bolt shank. The stationary die has a center hole which accepts the round stock of the exact length required. A pre-set movable pin inside the stationary die allows the round stock to travel into the die the exact distance required for the desired length of the bolt shank, leaving the exact length of round stock protruding from the die to form the bolt head or upset. The head is formed by one or more movable dies forming the round stock into the desired shape. The bolt in rivet form is then ejected from the stationary die and threads are then rolled or cut into the bolt shank.
Although the cold heading process is the most economical, it has the limitation that the upset limit should not be greater than 41/2 diameters of stock; that is, the volume limit to form the upset in terms of length of stock cannot exceed 41/2 times the diameter of the stock. If the ratio of upset is greater than this recommended amount, the efficiency of the cold heading process is defeated, and when it is desired that bolts have enlarged or thickened heads, they must be formed by other processes which as stated above have undesirable features.
All of the processes for forming bolts have a further disadvantage in that it is not possible or at least it is not economically feasible to provide a head of different material than the metal in the shank. Such combinations of metal or material may be desired in certain fastener applications.